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(#) Unsafe Protected `BroadcastReceiver`

!!! WARNING: Unsafe Protected `BroadcastReceiver`
   This is a warning.

Id
:   `UnsafeProtectedBroadcastReceiver`
Summary
:   Unsafe Protected `BroadcastReceiver`
Severity
:   Warning
Category
:   Security
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   1.5.0 (November 2015)
Affects
:   Kotlin and Java files and manifest files
Editing
:   This check runs on the fly in the IDE editor
See
:   https://goo.gle/UnsafeProtectedBroadcastReceiver
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/UnsafeBroadcastReceiverDetector.java)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UnsafeBroadcastReceiverDetectorTest.java)

`BroadcastReceiver`s that declare an intent-filter for a
protected-broadcast action string must check that the received intent's
action string matches the expected value, otherwise it is possible for
malicious actors to spoof intents.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/TestReceiver.java:10:Warning: This broadcast receiver
declares an intent-filter for a protected broadcast action string, which
can only be sent by the system, not third-party applications. However,
the receiver's onReceive method does not appear to call getAction to
ensure that the received Intent's action string matches the expected
value, potentially making it possible for another actor to send a
spoofed intent with no action string or a different action string and
cause undesired behavior. [UnsafeProtectedBroadcastReceiver]
    public void onReceive(Context context, Intent intent) {
                ---------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`AndroidManifest.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="test.pkg"
    android:versionCode="1"
    android:versionName="1.0" &gt;

    &lt;uses-sdk android:minSdkVersion="14" /&gt;

    &lt;application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" &gt;
        &lt;receiver
            android:label="@string/app_name"
            android:name=".TestReceiver" &gt;
                &lt;intent-filter&gt;
                    &lt;action android:name="android.intent.action.BOOT_COMPLETED"/&gt;
                &lt;/intent-filter&gt;
        &lt;/receiver&gt;
    &lt;/application&gt;

&lt;/manifest&gt;

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/TestReceiver.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class TestReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
    }

    // Anonymous classes should NOT be counted as a must-register
    private static BroadcastReceiver sample() {
        return new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
            }
        };
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UnsafeBroadcastReceiverDetectorTest.java)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `UnsafeBroadcastReceiverDetector.testBroken`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Adding the suppression attribute
  `tools:ignore="UnsafeProtectedBroadcastReceiver"` on the problematic
  XML element (or one of its enclosing elements). You may also need to
  add the following namespace declaration on the root element in the
  XML file if it's not already there:
  `xmlns:tools="http://schemas.android.com/tools"`.

  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;manifest xmlns:tools="http://schemas.android.com/tools"&gt;
      ...
      &lt;receiver tools:ignore="UnsafeProtectedBroadcastReceiver" .../&gt;
    ...
  &lt;/manifest&gt;
  ```

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("UnsafeProtectedBroadcastReceiver")
  fun method() {
     problematicStatement()
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("UnsafeProtectedBroadcastReceiver")
  void method() {
     problematicStatement();
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection UnsafeProtectedBroadcastReceiver
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="UnsafeProtectedBroadcastReceiver" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'UnsafeProtectedBroadcastReceiver'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore UnsafeProtectedBroadcastReceiver ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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